Unconjugated plasma estriol (E3) will be measured in 500-600 pregnant women at or around 31, 33, 35, 36, 37 and 38 weeks of gestation. These women with apparently uncomplicated pregnancies at the time of enrollment into the study will be randomly divided into a study and a control group. Patients in the study group will be referred for additional antepartum fetal evaluation if plasma E3 levels are abnormal. Plasma E3 levels in the control group will not influence clinical management. Labor, delivery and fetal outcome of study and control group will be compared. The efficacy of serial twice-weekly plasma E3 assays in the clinical management of prolonged pregnancies will be compared with that of antepartum fetal heart rate testing in a randomized prospective study involving a total of 200 patients. Twice-weekly plasma E3 assays will be used in the management of patients at or beyond term whose pregnancies are poorly dated in order to evaluate whether plasma E3 can be used to distinguish between those gravidas who may continue their pregnancies and those who need additional antepartum fetal evaluation and delivery. Plasma E3 will be measured twice weekly in patients with intrauterine growth retardation (IUGR) whose management is based upon other antepartum fatal evaluation to evaluate whether plasma E3 may be of clinical value in IUGR.